The majority of the present day lubricants are derived from fossil fuels. These lubricants cause damage to the environment, and moreover, they are extracted from non-renewable resources. Therefore there is an enormous amount of need for research on environmentally adaptable lubricants that are extracted from non-conventional sources of energy. Polysaccharides have characteristics of semi-flexible/rigid molecules and thereby exhibit shear thinning and elastic behavior even at high shear rates. Experimental literature on polysaccharide tribology is confined to friction, wear and rheology of polysaccharides in solution. However, molecular-level understanding of their mechanisms is still lacking, which is important to design efficient polysaccharide lubricants. Molecular Dynamics (MD) simulations can provide a detailed atomistic picture of polysaccharide structure and polysaccharide-metal interactions, which can aid us in the design of new polysaccharide based lubricants.<br/>Experimentally, it has been shown that sodium carboxymethyl cellulose (NaCMC) dispersed in polyethylene glycol (PEG) and water solution possess promising tribological properties. It has been hypothesized that the electrostatic interactions between NaCMC and water improves the solution stability whereas the hydrophobic groups on the polysaccharide chains aids in increasing the solution viscosity. However, molecular-level understanding of the frictional forces, structure of lubricant during the shearing process, surface-lubricant interactions and interfacial characteristics of metal surfaces is still lacking, which will assist in testing the aforementioned hypothesis. Here, atomistic non-equilibrium molecular dynamics (NEMD) simulations were employed to investigate the tribological properties of NaCMC with PEG+water solution as base fluid. Two sets of independent simulations were carried out to compare the triological properties of PEG+water base fluid and NaCMC+PEG+water lubricant. NEMD simulations were also carried out at different normal loads ranging from 0.1 to 1 GPa and shearing velocities ranging from 1 to 20 m/s. The lubricant was confined between two slabs made of BCC iron. Analysis including Coefficient of friction, frictional forces, velocity profiles, density profiles and radial distribution functions (RDF) was performed.

Investigation of tribological properties of polysaccharides based green lubricants using non-equilibrium molecular dynamics simulations

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